U.S. patent application number 12/887655 was filed with the patent office on 2012-03-22 for method and apparatus for estimating battery capacity of a battery.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Mutasim A. Salman, Kwang-Keun Shin, Xidong Tang, Yilu Zhang.
Application Number | 20120072145 12/887655 |
Document ID | / |
Family ID | 45818501 |
Filed Date | 2012-03-22 |
United States Patent
Application |
20120072145 |
Kind Code |
A1 |
Zhang; Yilu ; et
al. |
March 22, 2012 |
Method and Apparatus for Estimating Battery Capacity of a
Battery
Abstract
A method is provided for determining a battery capacity for a
vehicle battery. Open circuit voltages of a vehicle battery are
measured during ignition startups. A battery parameter is estimated
for the vehicle battery that is a function of a present open
circuit voltage measurement for a present ignition startup, a
function of at least one open circuit voltage observation of a
previous ignition startup, a function of a current draw integration
over a time period from a previous ignition startup event to a
present ignition startup event, and a function of an adjustment
factor. A battery parameter is determined based on a new battery.
The battery capacity is calculated as function of the battery
parameter for the vehicle battery and the battery parameter for the
new battery.
Inventors: |
Zhang; Yilu; (Northville,
MI) ; Shin; Kwang-Keun; (Rochester Hills, MI)
; Tang; Xidong; (Sterling Heights, MI) ; Salman;
Mutasim A.; (Rochester Hills, MI) |
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
45818501 |
Appl. No.: |
12/887655 |
Filed: |
September 22, 2010 |
Current U.S.
Class: |
702/63 |
Current CPC
Class: |
H01M 10/44 20130101;
G01R 31/3828 20190101; Y02E 60/10 20130101; G01R 31/3648
20130101 |
Class at
Publication: |
702/63 |
International
Class: |
G06F 19/00 20060101
G06F019/00; G01R 31/36 20060101 G01R031/36 |
Claims
1. A method of determining a battery capacity for a vehicle
battery, the method comprising the steps of: measuring open circuit
voltages of a vehicle battery during ignition startups; estimating
a battery parameter for the vehicle battery that is a function of a
present open circuit voltage measurement for a present ignition
startup, a function of at least one open circuit voltage
observation of a previous ignition startup, a function of a current
draw integration over a time period from a previous ignition
startup event to a present ignition startup event, and a function
of an adjustment factor; determining a battery parameter based on a
new battery; and calculating the battery capacity as function of
the battery parameter for the vehicle battery and the battery
parameter for the new battery.
2. The method of claim 1 wherein the battery parameter of the
vehicle battery is a function of a previous battery parameter
observation and a present estimated battery parameter.
3. The method of claim 2 wherein estimating a battery parameter for
the vehicle battery is represented by the following formula:
.theta. ^ k = .lamda. .theta. .theta. ^ k - 1 + ( 1 - .lamda.
.theta. ) V oc ( t k ) - V ^ oc ( t k - 1 ) .intg. t k - 1 t k I t
##EQU00012## where {circumflex over (.theta.)}.sub.k-1 is a
previous battery parameter observation, V oc ( t k ) - V ^ oc ( t k
- 1 ) .intg. t k - 1 t k I t ##EQU00013## a current battery
parameter observation, where V.sub.oc (t) is the present open
circuit voltage measurement at the k.sub.th ignition start,
{circumflex over (V)}.sub.oc (t.sub.k-1) is a previous open circuit
voltage observation, {circumflex over (.theta.)}.sub.k-1 is the
battery parameter of the vehicle battery estimated at a previous
ignition start, I is a current draw from the vehicle battery, and
.lamda..sub..theta. is an adjustment factor.
4. The method of claim 3 wherein the adjustment factor for the
battery parameter is a function of a time that an ignition key is
off and is represented by the following formula:
.lamda..sub..theta.=e.sup.-t.sup.off.sup.(t.sup.k.sup.)/.tau..sup..theta.-
.
5. The method of claim 3 wherein the battery capacity of the
battery is determined from the following formula:
Q.sub.actual=Q.sub.new(.theta..sub.new/{circumflex over
(.theta.)}.sub.k) where Q.sub.actual is the estimated actual
estimated battery capacity of the vehicle battery, Q.sub.new is a
battery capacity based on a new battery, .theta..sub.new is a
battery parameter based on a new battery, and {circumflex over
(.theta.)}.sub.k is the estimated battery parameter of the vehicle
battery.
6. The method of claim 5 wherein the battery parameter for the
vehicle battery, the battery parameter for the new battery, and the
charge capacity for the new battery are normalized at a respective
temperature.
7. The method of claim 3 wherein the present open circuit voltage
measurement, the previous open circuit voltage observation, and the
battery parameter are normalized at a respective temperature.
8. The method of claim 1 wherein the battery capacity of the
vehicle battery is displayed to user of the vehicle via a display
device.
9. The method of claim 1 wherein a representation of the battery
capacity of the battery is displayed to user of the vehicle via a
display device.
10. A system for determining a battery capacity for a vehicle
battery comprising: a battery; at least one component for drawing
power from the battery; a voltmeter for measuring an open circuit
voltage of the battery at ignition start sequences; a current
sensor for sensing current drawn from the battery; and a control
module for determining a battery parameter for the vehicle battery
that is a function of a present open circuit voltage measurement
for a present ignition startup, a function of at least one open
circuit voltage observation of a previous ignition startup, a
function of a current draw integration over a time period from a
previous ignition startup event to a present ignition startup
event, and a function of an adjustment factor, the control module
further determining a battery parameter based on a new battery, the
control module calculating the battery capacity as function of the
battery parameter for the vehicle battery and a function of the
battery parameter for the new battery.
11. The system of claim 11 wherein the control module estimating a
battery parameter for the vehicle battery is represented by the
following formula: .theta. ^ k = .lamda. .theta. .theta. ^ k - 1 +
( 1 - .lamda. .theta. ) V oc ( t k ) - V ^ oc ( t k - 1 ) .intg. t
k - 1 t k I t ##EQU00014## where .lamda..sub..theta.{circumflex
over (.theta.)}.sub.k-1 is the previous battery parameter
observation and V oc ( t k ) - V ^ oc ( t k - 1 ) .intg. t k - 1 t
k I t ##EQU00015## a current battery parameter observation, where
V.sub.oc (t) is the present open circuit voltage measurement at a
k.sub.th ignition start, {circumflex over (V)}.sub.oc (t.sub.k-1)
is a previous open circuit voltage observation, {circumflex over
(.theta.)}.sub.k-1 is the battery parameter of the vehicle battery
estimated at a previous ignition start, I is a current draw from
the vehicle battery, and .lamda..sub..theta. is an adjustment
factor.
12. The system of claim 12 wherein the control module determines
the adjustment factor for the battery parameter of the vehicle
battery as a function of a time that an ignition key is off,
wherein the adjustment factor is determined by the following
formula:
.lamda..sub..theta.=e.sup.-t.sup.off.sup.(t.sup.k.sup.)/.tau..sup..theta.-
.
13. The system of claim 12 wherein the control module normalizes
the present open circuit voltage measurement at the k.sub.th
ignition start, the previous open circuit voltage observation, and
the battery parameter of the vehicle battery are normalized at a
respective temperature.
14. The system of claim 11 wherein the battery capacity of the
battery is determined from the following formula:
Q.sub.actual=Q.sub.new(.theta..sub.new/{circumflex over
(.theta.)}.sub.k) where Q.sub.actual is the estimated battery
capacity of the vehicle battery, Q.sub.current.sup.T is a
normalized battery capacity based on a new battery, .theta..sub.new
is a battery parameter based on a new battery, and {circumflex over
(.theta.)}.sub.k is the estimated battery parameter of the vehicle
battery.
Description
BACKGROUND OF INVENTION
[0001] An embodiment relates generally to determining battery
capacity within a vehicle.
[0002] Determining a battery capacity for a battery can be
performed utilizing various techniques utilizing coulomb counting
or parameter estimations techniques. Coulomb counting involves the
use of one measurement (i.e., one open circuit voltage reading) to
estimate the battery state-of-charge. The accuracy of the open
circuit voltage is critical to determining a state of charge. If
there is measurement error, then the state-of-charge estimation
will be in error by basically the factor of the measurement
error.
[0003] Moreover, coulomb counting techniques utilizing charge
efficiency and battery capacity to determine state-of-charge often
use the standard manufacturing specification values for a new
battery values throughout the estimation process for the life of
the battery. Over time the battery ages and charge efficiency and
battery capacity changes as well thereby creating error in the
state-of-charge estimation.
[0004] Current parameter estimation techniques require excitations
which are not necessarily available on conventional vehicles.
SUMMARY OF INVENTION
[0005] An advantage of an embodiment is the determination of a
battery capacity where error in estimating the battery capacity is
reduced by utilizing the integration of both present and previous
open circuit voltage measurements/estimations and current draws.
Deficiencies of prior art techniques are overcome by not solely
basing the determination of the battery capacity on a new battery.
Since battery characteristics change over a life of the battery,
utilizing both present and past battery characteristic
measurements/estimations provide a more comprehensive analysis as
to how the battery is changing over a course of time which reduces
any anomalies that may occur in a single
measurement/estimation.
[0006] An embodiment contemplates a method of determining a battery
capacity for a vehicle battery. Open circuit voltages of a vehicle
battery are measured during ignition startups. A battery parameter
is estimated for the vehicle battery that is a function of a
present open circuit voltage measurement for a present ignition
startup, a function of at least one open circuit voltage
observation of a previous ignition startup, a function of a current
draw integration over a time period from a previous ignition
startup event to a present ignition startup event, and a function
of an adjustment factor. A battery parameter is determined based on
a new battery. The battery capacity is calculated as function of
the battery parameter for the vehicle battery and the battery
parameter for the new battery.
[0007] An embodiment contemplates a system for determining a
battery capacity for a vehicle battery. The system includes a
battery, at least one component for drawing power from the battery,
a voltmeter for measuring an open circuit voltage of the battery at
ignition start sequences, and a current sensor for sensing current
drawn from the battery. The system further includes a control
module for determining a battery parameter for the vehicle battery
that is a function of a present open circuit voltage measurement
for a present ignition startup, a function of at least one open
circuit voltage observation of a previous ignition startup, a
function of a current draw integration over a time period from a
previous ignition startup event to a present ignition startup
event, and a function of an adjustment factor. The control module
further determines a battery parameter based on a new battery. The
control module calculates the battery capacity as function of the
battery parameter for the vehicle battery and a function of the
battery parameter for the new battery.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a block diagram system for estimating a
state-of-charge (SOC) and battery capacity of a battery.
[0009] FIG. 2 is a timeline schematic illustrating time instances
for determining open circuit voltages.
[0010] FIG. 3 a flowchart of a method for determining a state of
charge (SOC) of a battery and battery capacity.
DETAILED DESCRIPTION
[0011] FIG. 1 illustrates a block diagram of an embodiment of a
vehicle 10 incorporating a state-of-charge (SOC) and battery
capacity estimation system. It should be understood that the
vehicle may include, but is not limited to, hybrid vehicles,
internal combustion vehicles, and electric vehicles or any
machinery that utilizes batteries. The vehicle 10 includes a
battery pack 12 having a single battery or a plurality of
individual battery modules. For example, an embodiment may include
a plurality of batteries connected in series to produce a high
voltage nominal voltage or a vehicle may include a single 12 volt
battery producing a 14 volt nominal voltage for an internal
combustion vehicle. The state-of-charge and battery capacity
estimation technique described herein may be applicable to variety
of battery types, including but not limited to, nickel metal
hydride (NiMH) batteries, lead acid batteries, or lithium ion
batteries.
[0012] The vehicle battery 12 is electrically coupled to a
plurality of devices 14 which utilize the battery as a power
source. The vehicle 10 may further include a current sensor 16, and
voltage meter 18, and a control module 20.
[0013] The plurality of devices 14 include, but are not limited to,
power outlets adapted to an external plug in device, accessories,
components, subsystems, and systems of a vehicle. The current
sensor 16 is used to monitor the current leaving the vehicle
battery 12. The voltmeter 18 measures a voltage so that an open
circuit voltage may be determined. A control module 20, or similar
module, obtains, derives, monitors, and/or processes a set of
parameters associated with vehicle battery 12. These parameters may
include, without limitation, current, voltage, state-of-charge
(SOC), battery capacity, battery internal resistances, battery
internal reactance, battery temperature, and power output of the
vehicle battery. The control module 20 includes an algorithm, or
like, for executing a vehicle state-of-charge and battery capacity
estimation technique. In a hybrid vehicle or electric vehicle, it
is typical that a current sensor is integral to the control
module.
[0014] To enhance battery charging control and vehicle power
management, the open circuit voltage V.sub.oc is used to estimate
the SOC. The SOC of the battery is estimated utilizing a startup
SOC and a run SOC change. The formula for the SOC of the battery is
represented as follows:
S.sub.oc=SOC.sub.startup+SOC.sub.running=f(V.sub.oc(0),T)+.theta..intg.I-
dt (1)
where f(V.sub.oc (0),T) is the startup SOC that is a function of
the open circuit voltage and temperature, and .theta..intg.Idt is
the run SOC change that is a function of a battery parameter
.theta. and previous current data integration. The battery
parameter .theta.(=c/Q) is a function of battery charge efficiency
c and battery capacity Q.
[0015] The open circuit voltage V.sub.oc is a key element in
determining the SOC. Therefore the following embodiment will focus
on how V.sub.oc is derived and utilized in determining
SOC.sub.startup and SOC.sub.running.
[0016] FIG. 2 illustrates a timeline for estimating a plurality of
open circuit voltages for SOC.sub.startup which takes into
consideration historical data. Historical data relates to previous
instances of time at which an ignition off and ignition on event is
detected and battery characteristics are observed. The term
observed used herein refers to measured and/or estimated values
based on measurements. A timing sequence of continuous ignition on
I.sub.n and ignition off I.sub.f events is shown generally at 20.
Timeline 22 illustrates each of the time instances when the
ignition transitions from an ignition-off to an ignition-on (e.g.,
t.sub.k-2,t.sub.k-1,t.sub.k). Based on the different time
instances, an open circuit voltage may be determined for each time
instance taking into consideration not only the present open
circuit voltage measurement, but also previous open circuit voltage
measurements for estimating a more precise open circuit voltage
value at the k.sub.th ignition event. Formulas for the time
instances t.sub.k-2,t.sub.k-1,t.sub.k shown in FIG. 2 are
represented by the following formulas:
V ^ oc ( t k , t k ) = V oc ( t k ) ( 2 ) V ^ oc ( t k , t k - 1 )
= V oc ( t k - 1 ) + .theta. .intg. t k - 1 t k I t ( 3 ) V ^ oc (
t k , t k - 2 ) = V oc ( t k - 2 ) + .theta. .intg. t k - 1 t k I t
+ .theta. .intg. t k - 2 t k - 1 I t ( 4 ) ##EQU00001##
[0017] When taking into consideration the past observations, a
weighted average is obtained utilizing an adjustment factor
.lamda.. The adjustment factor .lamda. weights the open circuit
voltage estimation based on the duration of the key-off time or the
key-on time. It should be understood that the technique described
herein for determining the adjustment factor is only one embodiment
of how the adjustment factor may be determined and that other
techniques used to determine the adjustment factor may be applied
herein without deviating from the scope of the invention. The
formula for determining the open circuit voltage utilizing the
adjustment factor is represented by the following formula:
V ^ oc ( t k ) = .lamda. { V ^ ( t k - 1 ) + .theta. ^ .intg. t k -
1 t k i t } + ( 1 - .lamda. ) V oc ( t k ) . ( 5 ) ##EQU00002##
where
{ V ^ ( t k - 1 ) + .theta. ^ .intg. t k - 1 t k i t }
##EQU00003##
represents the estimation based on previous observation
(t.sub.k-n), and (1-.lamda.)V.sub.oc(t.sub.k) represents a present
observation (t.sub.k).
[0018] Therefore, if the key-off time is too short, then a greater
emphasis is placed on the estimated value in which the adjustment
factor would be preferably close to 1. If the key-off time is
greater than a predetermined time value, then a greater emphasis is
placed on the current observation, and the adjustment factor would
be preferably close to 0. As a result, the following formula is
used to determine the adjustment factor .lamda. which is a function
of the time off. The adjustment factor .lamda. for the open circuit
voltage is represented by the following formula:
.lamda.=e.sup.-t.sup.off.sup.(t.sup.k.sup.)/.tau. (6)
where t.sub.off is a time from when the ignition key is turned off
to a time the ignition is turned on, t.sub.k is a time the ignition
key is turned on at the k.sub.th ignition interval, and .tau. is a
time constant.
[0019] The battery parameter .theta. is commonly determined by a
ratio of the charge efficiency and the battery capacity. Charge
efficiency and battery capacity values are typically nominal values
based on a new battery. However, such parameters change as the
battery ages, and as a result, are not robust factors for
determining the battery parameter .theta.. Since these parameters
change with age, the battery parameter .theta. should be estimated
periodically. To estimate the battery parameter .theta. on a
periodic basis (e.g., once a month), the battery parameter .theta.
is solved for utilizing the open circuit voltage formula which is
represented as follows:
V ^ oc ( t k ) = V ^ oc ( t k - 1 ) + .theta. ^ k .intg. t k - 1 t
k I t . ( 7 ) ##EQU00004##
By modifying the open circuit voltage {circumflex over (V)}.sub.oc
(t.sub.k) to solve for .theta., the resulting battery parameter
.theta. is represented as follows:
.theta. ^ k = V oc ( t k ) - V ^ oc ( t k - 1 ) .intg. t k - 1 t k
I t ( 8 ) ##EQU00005##
To compensate for short ignition key-off times, an adjustment
factor is incorporated in the battery parameter estimation formula.
The adjustment factor for the battery parameter .lamda..sub..theta.
is represented by the following formula:
.lamda..sub..theta.=e.sup.-t.sup.off.sup.(t.sup.k.sup.)/.tau..sup..theta-
. (9)
The resulting formula for the battery parameter is as follows:
.theta. ^ k = .lamda. .theta. .theta. ^ k - 1 + ( 1 - .lamda.
.theta. ) V oc ( t k ) - V ^ oc ( t k - 1 ) .intg. t k - 1 t k I t
( 10 ) ##EQU00006##
where {circumflex over (.theta.)}.sub.k-1 is the previous battery
parameter estimation and
V oc ( t k ) - V ^ oc ( t k - 1 ) .intg. t k - 1 t k I t
##EQU00007##
a present battery parameter estimation.
[0020] Due to temperature differences when measurements for current
and previous open circuit voltage are obtained, the estimation
technique generated herein requires normalization between the open
circuit voltage measurements. That is, each open circuit voltage
(i.e., both present and previous), must be normalized at a standard
temperature so that present observations and past observations can
be cooperatively utilized. As a result, each open circuit voltage
for a respective ignition event is converted to an open circuit
voltage based on a normalized temperature. The conversion may be
performed utilizing an algorithm, lookup table, or the like. For
example, a normalized formula utilizing a standardized temperature,
such as 25 degrees, is represented as follows:
V ^ oc 25 ( t k ) = .lamda. { V ^ oc 25 ( t k - 1 ) + .theta. ^ k -
1 25 .intg. t k - 1 t k i t } + ( 1 - .lamda. ) V oc 25 ( t k ) . (
11 ) ##EQU00008##
The battery parameter using normalized temperatures is as
follows:
.theta. ^ k 25 = .lamda. .theta. .theta. ^ k - 1 25 + ( 1 - .lamda.
.theta. ) V oc 25 ( t k ) - V ^ oc 25 ( t k - 1 ) .intg. t k - 1 t
k I t . ( 12 ) ##EQU00009##
As a result, the open circuit voltage for the SOC of the vehicle
battery can be represented by the following formula:
{circumflex over (V)}.sub.oc.sup.25(t,t.sub.k)={circumflex over
(V)}.sub.oc.sup.25(t.sub.k)+.theta..sub.k.sup.25.intg..sub.t.sub.k.sup.tI-
dt. (13)
[0021] Once the normalized open circuit voltage {circumflex over
(V)}.sub.oc.sup.25 (t, t.sub.k) for the SOC of the battery is
determined, the normalized open circuit voltage is converted back
to the open circuit voltage at the current temperature and is
represented by {circumflex over (V)}.sub.oc(t).
[0022] The SOC charge of the battery is determined utilizing
{circumflex over (V)}.sub.oc(t) that incorporates estimations of
both current measurements and previous measurements. The other
factors in determining SOC can be basically grouped as a linear
mapping constant. As a result, the SOC of the vehicle battery at
the present instance of time may be represented by the following
formula:
SOC(t)=f({circumflex over (V)}.sub.oc(t),T) (14)
where {circumflex over (V)}.sub.oc(t) is the estimated open circuit
voltage of the battery using current measurements and previous
measurements, and T is a respective temperature at the time of the
measurement.
[0023] The battery capacity Q is also determined utilizing current
measurements and battery parameters. The battery capacity is
derived utilizing the following formula represented by:
Q.sub.actual.sup.25=Q.sub.new.sup.25(.theta..sub.new.sup.25/.theta..sub.-
k.sup.25) (15)
where Q.sub.actual.sup.25 is the normalized estimated battery
capacity of the battery, Q.sub.new.sup.25 is a normalized battery
capacity of a new battery, .theta..sub.new.sup.25 is a normalized
battery parameter of a new battery, and {circumflex over
(.theta.)}.sub.k.sup.25 is the normalized estimated battery
parameter as a function of an adjustment factor. It should be
understood that in deriving the battery capacity, estimations must
be derived using a standard temperature (e.g., 25 degrees). The
formula for determining the battery parameter at the k.sub.th
ignition start is represented by the following formula:
.theta. ^ k 25 = .lamda. .theta. .theta. ^ k - 1 25 + ( 1 - .lamda.
.theta. ) V oc 25 ( t k ) - V ^ oc 25 ( t k - 1 ) .intg. t k - 1 t
k I t ( 16 ) ##EQU00010##
[0024] The battery capacity as shown in equation (15) may be
simplified to the following formula:
Q.sub.actual.sup.25=c.sub.new/.theta..sub.k.sup.25 (17)
where c.sub.new is the charge efficiency for a new battery.
Simplifying the battery capacity to the form shown in equation (17)
is as follows. The battery parameter for a new battery is
represented as follows:
.theta..sub.new=c.sub.new/Q.sub.new. (18)
The formula for battery parameter estimation shown in equation 18
is a valid estimation when the charge efficiency and battery
capacity of the battery is actually known. As a battery ages, the
charge efficiency and battery capacity of an aging battery changes.
Therefore, a battery parameter estimation for a new battery can be
determined using equation (18). Such values (e.g., c.sub.new and
Q.sub.new) for determining the characteristics of the new battery
may be obtained by the battery manufacturer or performing a bench
test (i.e., fully discharging a battery and fully charging a
battery). A new battery is a battery that is newly manufactured and
has had very limited cycling occur (e.g., charging/discharging).
Referring again to equation (15), the formula of the battery
parameter .theta..sub.new determined in equation (18) is
substituted in equation (15) resulting in the following
formula:
Q actual = Q new ( ( c new Q new ) .theta. k 25 ) , ( 19 )
##EQU00011##
As a result, equation (19) may be simplified to the formula shown
in equation (17) where Q.sub.actual=c.sub.new/.theta..sub.k.
[0025] FIG. 3 illustrates a flowchart for a technique for
estimating the SOC and battery capacity utilizing V.sub.oc data. In
step 30, a first key-on event is initiated. The first key-on
represents a time when the vehicle ignition is first started and
data is collected. The first key-on event may also represent a time
when the vehicle ignition is started directly after the vehicle
battery is replaced and data is obtained for the new battery. In
this manner, previous data relating to past battery operating
conditions and parameters would no longer be valid since the new
battery would have different charging and efficiency
characteristics (e.g., charge efficiency values and battery
capacity values).
[0026] In step 31, the measurable parameters and estimated
parameters are initialized. That is, at the initiation of a new
vehicle startup or when the battery is replaced, all variables for
the each of the formulas described above are re-set to their
initial conditions. For example, k=0, .lamda.=0,
.lamda..sub..theta.=1, .theta..sub.0.sup.25=.theta..sub.new.sup.25,
{circumflex over (V)}.sub.oc.sup.25(0)=13V,
.DELTA.Q=Q.sub.new.sup.25.
[0027] In step 32, the present open circuit voltage V.sub.oc
(t.sub.k) and the battery temperature T are measured.
[0028] In step 33, the open circuit voltage V.sub.oc (t.sub.k) is
converted to an open circuit voltage at a standard temperature
V.sub.oc.sup.25 (t.sub.k). The conversion may be performed using an
algorithm or a lookup table.
[0029] In step 34, the startup voltage is updated using the formula
set forth in equation (11).
[0030] In step 35, the battery parameter is updated using the
formula set forth in equation (12).
[0031] In step 36, the battery capacity is updated using the
formula set forth in equation (15).
[0032] In step 37, the current integration .intg.Idt is reset to
zero.
[0033] In step 38, a determination is made whether the ignition key
is in the key-off position. If the ignition is in the key-off
position, then the routine proceeds to step 39; otherwise the
routine proceeds to step 47.
[0034] In step 39, the key-off time is reset to zero (t.sub.off=0).
This initiates a counter for determining how long the ignition is
in the key-off position.
[0035] In step 40, a determination is made whether the ignition key
is in the key-on position. If the ignition key is not in the key-on
position, then the routine proceeds to step 41.
[0036] In step 41, the routine waits for a period of time before
updating the key-off time.
[0037] In step 42, the key-off time is updated. The key-off time is
represented by the following formula:
t.sub.off=t.sub.off+.DELTA.t.sub.off
where t.sub.off is a summation of the key-off time since the
resetting the key-off time, and .DELTA.t.sub.off is the additive
time period elapsed in step 41.
[0038] In step 43, the current measurement (I) of the battery is
measured.
[0039] In step 44, the current integration is updated which
incorporates the present current measurement with the past current
measurements. The routine proceeds back to step 40.
[0040] In step 40, if the determination is made that the ignition
key is on, then the routine proceeds to step 45, otherwise, the
routine proceeds to step 41.
[0041] In step 45, a key-on cycle count is updated. The key-on
cycle count is the number of times the ignition key has been turned
on since system initialization in step 31. Each time the ignition
key is turned on, the count is increased by 1.
[0042] In step 46, the adjustment factor is determined for the open
circuit voltage as set forth in equation (6) and the adjustment
factor is determined for the battery parameter as set forth in
equation (8). Thereafter, a return is made to step 32 to execute
steps 32-38 as described above.
[0043] In step 38, if the determination is made that the ignition
key is not in the key-off position, then the routine proceeds to
step 47.
[0044] In step 47, the current (I) leaving the battery and the
temperature (T) is measured.
[0045] In step 48, the current integration is updated based on the
past to present measurements.
[0046] In step 49, the running open circuit voltage {circumflex
over (V)}.sub.oc.sup.25 (t) at the standard temperature is updated
using the formula set forth in equation (13).
[0047] In step 50, the running open circuit voltage {circumflex
over (V)}.sub.oc.sup.25 (t) is converted back to a running open
circuit voltage {circumflex over (V)}.sub.oc (t) at the present
temperature using an algorithm or a lookup table.
[0048] In step 51, the SOC for the battery at the present
temperature is determined using the formula set forth in equation
(14).
[0049] In step 52, a predetermined period of time elapses before
returning to step 38.
[0050] The battery capacity derived in step 36 and the SOC derived
step 51 are either displayed to the driver of the vehicle
identifying the condition of the battery or may be represented in
some other capacity for indicating the SOC and battery
capacity.
[0051] While certain embodiments of the present invention have been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
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